1. Field of the Invention
The present invention relates to an apparatus for displaying a visual acuity chart which displays visual chart images to an eye to be examined by using a half mirror and a concave mirror.
2. Description of Related Art
In conventional apparatus for displaying a visual acuity chart using a half mirror and a concave mirror, there are fixed distance apparatus in which visual chart images for an eye examination are displayed to an eye to be examined while the distance between the eye to be examined and the images is kept constant, and an infinity apparatus in which visual chart images for an eye examination are formed at infinity to be displayed to an eye to be examined.
However, the fixed distance apparatus for displaying a visual acuity chart has a problem, when the apparatus is placed in certain locations, for example, where an eye examination space is narrow. If a person to be examined cannot look at the visual charts from an appropriate position, an accurate eye examination cannot be carried out.
The infinity apparatus for displaying a visual acuity chart also has a problem. Although the freedom of locating the apparatus is high because parallel light beams are incident onto an eye to be examined from the visual charts, a visual acuity examination for the eye to be examined is normally carried out at an eye examination distance of 5 meters. As a result, differences in the adjusting power of the eye to be examined may occur to thereby cause excessive correction, and differences from a visual acuity value measured by other eye examination apparatus. Thus, an accurate eye examination can not be carried out as well.